Monday, 25 June 2018

Introducing ROCKETS: An executable MBSE process

What is the ROCKETS MBSE process?

I've decided to name my MBSE method ROCKETS. ROCKETS is a derivative of the the Harmony/SE method that uses executable MBSE with SysML and IBM Rational Rhapsody. It stands for Requirements Originating in the Context of Knowledge Executed as Transitions on Statecharts. It’s designed to be fun. To make it fun a couple of aspects are considered important:

  1. Automation, so that the user is focused on the creative aspects associated with solving the problem, rather than setting up the model.
  2. Systematic, the method splits the problem down. The adage is to take tiny steps rather than a giant leap.
  3. Team work. How people interact during the process is considered as important as the artefacts that are produced.

The approach is use case driven, and conforms to the original definition of a use case as:
“A description of a set of sequences of actions, including variants, that a system performs that yield an observable result of value to an actor” [Booch, Rumbaugh, Jacobson 1999] (where actors are entities outside of the system that gain value from or participate in the use case)

Importantly, use cases are stories about how the system is intended to be used. ROCKETS is therefore a method focused on concept of operations (CONOPS) modeling. CONOPS models describe clearly and concisely what the is to be accomplished and how it will be done using available resources. As such it is independent of aspects such as programming language and software design. We are trying to model who needs to do what, rather than how it is done.

What are the phases of the ROCKET process?

There are three phases to the ROCKET process:

  1. Payload definition.
  2. Launching the rocket(s).
  3. Assembling the space station.

The key challenge overcome from the ROCKETS process is the management of complexity; the division of responsibility across a team and between teams of engineers such that the task can be accomplished with productive use of resources. In practice these phases occur in parallel, as we can’t get the whole space station into a single rocket, we need to send up a series of rockets.

The space station analogy is a useful one because we can picture it as a series of components that are interconnected. Importantly, we might read the components as component owners. This is a systems engineering task to allocate work to different teams by deciding which team needs to do what.

Payload definition starts on the ground with the creation of functional system requirements that we intend to launch up to the space station. To get them to the space station we need to launch them. We do this with executable MBSE. Much like how we might hypothesis how a clock might work, executable MBSE involves building a simulation that we can interact with to test how the system may work. We then need to get the payload into space in a rocket where they will be assembled by a separate team.

What is the relationship to process standards?

ROCKETS process aligns directly with Sys.1 to Sys.5 of A-SPICE 3.

SYS.1 Requirements Elicitation
SYS.2 System Requirements Analysis
SYS.3 System Architectural Design
SYS.4 System Integration and Integration Test
SYS.5 System Qualification Test

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